The 32-year-old man fell ill after visiting a live poultry market several times to conduct research in southern Guangdong province, which borders Hong Kong. He died last Thursday, the ninth person to die of bird flu in China.
"He is an urban resident, he had no contact with farms or any poultry from the villages. His only exposure is the wet markets, which has poultry which are supposedly safe for consumption and safe for the public," Hong Kong's health minister York Chow said.
"And Guangdong province is one of the best (in China) in terms of supervising the control of avian flu. Since last year, it has immunized all its poultry through vaccination," he told a news conference.
Guangdong has not reported any outbreaks of the H5N1 avian flu virus in birds over the past year, and the man's death has heightened fears among experts that there might be poultry that are infected by the virus but which are not sickened by it.
"It's very conceivable that there are more cases," said Dr. Henk Bekedam, the WHO's representative for China.
"But we do not have the impression, at least from the central ministry, that they are hiding information from the outside world."
Rather, Dr. Bekedam said he believes China has a "capacity problem" in terms of its ability to conduct surveillance for infection in birds and detect all human cases, particularly those in which the virus triggers milder disease.